1. The Field of the Invention
The present invention relates generally to drilling devices and methods. In particular, the present invention relates to devices to prevent a core barrel from falling when being handled outside of a drill string.
2. The Relevant Technology
Core drilling (or core sampling) includes obtaining core samples of subterranean formations at various depths for various reasons. For example, a retrieved core sample can indicate what materials, such as petroleum, precious metals, and other desirable materials, are present or are likely to be present in a particular formation, and at what depths. In some cases, core sampling can be used to give a geological timeline of materials and events. As such, core sampling may be used to determine the desirability of further exploration in a particular area.
Wireline drilling systems are one common type of drilling system for retrieving a core sample. In a wireline drilling process, a core drill bit is attached to the leading edge of an outer tube or drill rod. A drill string is then formed by attaching a series of drill rods that are assembled together section by section as the outer tube is lowered deeper into the desired formation. A core barrel assembly is then lowered or pumped into the drill string.
Core barrel assemblies commonly include a core barrel for receiving the core, and a head assembly for attaching the core barrel assembly to the wireline. Typically, the core barrel assembly is lowered into the drill string until the core barrel reaches a landing seat on an outer tube or distal most drill rod. At this point a latch on the head assembly is deployed to restrict the movement of the core barrel assembly with respect to the drill rod. Once latched, the drill string is rotated, pushed, and/or vibrated into the formation, thereby causing a sample of the desired material to enter into the core barrel assembly.
Once the core sample is obtained, the core barrel assembly is retrieved from the drill string to obtain the core sample. Often a wireline assembly is used to remove the core barrel (and core sample) from the bottom of the drill string. For example, a wireline may be connected to an overshot assembly. The overshot can engage a spearhead assembly that is connected to the core barrel assembly. The overshot typically connects to spearhead assembly via an overshot latch mechanism, which allows the core barrel to be retrieved when the wireline is retracted. When the overshot and core barrel are within the drill string, the alignment between the overshot and core barrel is constrained, which allows the overshot latch mechanism to function correctly.
When retrieving a core sample, the wireline and hoist often elevate the core barrel assembly until it is completely extracted from the drill string. Once extracted from the drill string, the lower end of the core barrel assembly may be moved away from the borehole and the core sample retrieved. Once the overshot and the core barrel assembly are removed from the drill string, alignment between the overshot and the core barrel assembly may not be maintained. It is possible that extra loading may be applied to the overshot latch mechanism as the core barrel assembly is maneuvered away from the drill mast. The extra loading and/or misalignment of the overshot and the core barrel assembly may cause the overshot latch mechanism to fail. In the event that the overshot latch mechanism fails, the core barrel assembly can fall uncontrollably. Due to the close proximity of the drill operators to the drill string and retrieved core barrel, if a core barrel assembly falls there may be a high possibility of injuring an operator. Furthermore, a dropped core barrel assembly can damage the drilling equipment and/or the retrieved core sample.
Accordingly, there are a number of disadvantages in conventional core barrel retrieval systems and methods that can be addressed.